Electromagnetic metatl detector stations for finding ferromagnetic objects such as weapons carried by person into airports and other secured areas are well known in the art. Typically U.S. Pat. No. 3,971,983 July 27, 1976 to J. R. Jaquet provides such a system with the advantage that it is a passive system which works in different locations having different configuations of the earth's magnetic field.
In operation however, this and similar electromagnetic detectors have been found to produce false alarms particulary when sensitivity is set high enough to detect weapons etc. of small mass and/or to decrease the risks of passing weapons through undetected. Such false alarms cause relatively long delays in processing persons quickly through to board a flight, and tend to cause compromise sensitivity operation permitting weapons to be passed through a station escaping detection.
Furthermore even if sensitivity is high enough to detect a weapon while tolerating increased alarms, there is a possibility that a weapon will not be detected by prior art detection stations under certain conditions because of local variations in electromagnetic field configurations in different installations. The modification of such local electromagnetic configurations by local or environment personnel can permit shielding of weapons carried by a person through the detector station.
It is therefore the objective of this invention to improve the reliability of weapon detection in electromagnetic field metal detector stations, and to improve signal to noise ratios in detecting ferromagnetic objects of small mass.
Other objects, features and advantages of the invention will be found throughout the following description, claims and drawings.